TMC2209 stepper driver on an Arduino Uno

// A NEMA 17 on a TMC2209 SilentStepStick, from an Uno, with plain pulses.
//
//   TMC2209 STEP -> pin 2    DIR -> pin 3    EN -> pin 4
//   TMC2209 VIO -> 5V        GND -> GND
//   TMC2209 VM / GNDM -> 12 V,  M1A M1B and M2A M2B -> the motor's two coils
//
// The TMC2209 takes STEP and DIR like an A4988, but there is no RST or SLP to
// link, and with MS1 and MS2 left alone it is in 1/8 step, not full step: a
// 200 step motor takes 1600 pulses a turn. EN is active low.

const int STEP_PIN = 2;
const int DIR_PIN = 3;
const int EN_PIN = 4;
const int PER_TURN = 200 * 8;

void turn(bool forward) {
  digitalWrite(DIR_PIN, forward ? HIGH : LOW);
  for (int i = 0; i < PER_TURN; i++) {
    digitalWrite(STEP_PIN, HIGH);
    delayMicroseconds(5);
    digitalWrite(STEP_PIN, LOW);
    delayMicroseconds(620);
  }
}

void setup() {
  pinMode(STEP_PIN, OUTPUT);
  pinMode(DIR_PIN, OUTPUT);
  pinMode(EN_PIN, OUTPUT);
  digitalWrite(EN_PIN, LOW);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: TMC2209 at 1/8 step, one turn each way");
}

void loop() {
  turn(true);
  Serial.println("one turn forward");
  delay(500);
  turn(false);
  Serial.println("and back");
  delay(500);
}